This application relates to and incorporates herein by reference Japanese Patent Application No.2002-8897 filed on Jan. 17, 2002.
The present invention relates to electronic equipment that has two electronic circuit boards, such as a telematics electronic control unit (ECU).
Some electronic equipment for an automotive vehicle include a telematics electronic control unit (ECU). Telematics, a combination of telecommunication and informatics, is a system to provide various services of total communication integrated by the Global Positioning System (GPS), a radiotelephony, the Internet, and so on. For example, the telematics system provides a stolen-car location information service, which informs a car owner of the present location of the stolen-car, and a remote horn service, which informs a car owner of the present location of the parking car in a large parking lot by blaring a horn by remote control operation.
The telematics ECU is a terminal of mobile electronic equipment for an automotive vehicle to utilize the telematics system. To utilize the telematics system, the telematics ECU requires to stand by for receiving a radio wave communication, even when a main switch of the vehicle is turned off. Therefore, saving an electric power supply to the telematics ECU is desirable. In this aspect, it is preferred that a radio communication unit and a control unit in the telematics ECU are divided into two modules, and that the radio communication unit maintains an intermittent standby mode when the main switch is turned off. The radio communication unit communicates with an external unit via radio waves, and the control unit controls a telematics terminal operation.
Therefore, the telematics ECU is composed of two modules. One is a radio communication module, and the other is a control module. To achieve size reduction of the telematics ECU, two modules are piled up in a casing of the telematics ECU.
One example of the telematics ECU is shown in FIG. 3. In this telematics ECU, a casing 50 is composed of a base 2 and a cover 5. A radio communication unit 10 and a control unit 20 are assembled in the base 2 by screws 6.
The radio communication unit 10 is composed of a radio module board 1, a radio module shield case 4 that covers the upper and lower sides of the radio module board 1, and a joining connector 7a that is fixed to the radio module board 1. The radio module board 1 is attached to the base 2 by the screws 6. The lower side of the shield case 4 contacts the bottom of the base 2.
The radio module board 1 has an electronic circuit generating a predetermined electric power in case of transmitting radio waves. In this operation, the electronic circuit generates electromagnetic radiation and heat. The shield case 4, which is made of a metal or conducting material, shields the electromagnetic radiation generated by the radio module board 1. Moreover, the shield case 4 conducts the heat, which is generated by the radio module board 1, to the base 2 by heat conduction. The heat conduction from the shield case 4 promotes heat radiation of the telematics ECU.
The control unit 20 is composed of a vehicle interface board 3 and a joining connector 7b that is fixed to the vehicle interface board 3. The vehicle interface board 3 is overlapped over the radio communication unit 10 and attached to the base 2 by the screws 6. The joining connector 7b is joined to the joining connector 7a that is fixed to the radio module board 1. Therefore, the vehicle interface board 3 electrically contacts the radio module board 1 through the joining connectors 7a, 7b. 
When the cover 5 is opened so as to look down at the radio communication unit 10, the radio communication unit 10 is completely hidden behind the vehicle interface board 3. As a result, a physical contact of the joining connectors 7a, 7b is not visible, after the radio communication unit 10 and the control unit 20 are assembled in the base 2.
The radio module board 1 is required to be readily exchangeable for a model change or an upgrade of a radio communication system. However, it is difficult to exchange the radio module board 1, because the vehicle interface board 3 prevents to exchange the radio module board 1. As a result, the telematics ECU has a maintainability problem.
Furthermore, the heat generated by the radio module board 1 conducts to the vehicle interface board 3 through the shield case 4. Therefore, the heat radiation is limited by a heat accumulation of the vehicle interface board 3, and the heat is not radiated outside substantially. To avoid the heat accumulation and to promote an efficiency of heat radiation, it is proposed to arrange the radio communication unit 10 and the control unit 20 side by side on the same plane, and both upper and lower sides of the shield case 4 contacts both the base 2 and the cover 5, respectively. However, in this arrangement, the telematics ECU is enlarged in size.
The present invention has an object to reduce size and to promote a maintainability of electronic equipment, which is composed of two electronic circuit boards. The present invention has another object to promote an efficiency of heat radiation of electronic equipment.
According to the present invention, electronic equipment is constructed of two electronic circuit boards and a casing. A first electronic circuit board is, for example, for a radio communication unit, and a second electronic circuit board is, for example, for a control unit. The two electronic circuit boards are piled up in the casing to face each other. The first board has a portion that does not face the second board. The first board is attached to the casing, and heat generated by the first board is conducted to the upper and lower sides of the casing by heat conduction through the portion.